Added itemWithLabel:action:

Buttons can be initialised at the same time as they are used.
Updated the README to include shorter form RIButton creation
Merge pull request #20 from p-l/master

Added shortcut to create RIButton with both label and action
Merge branch 'master' of git://github.com/jivadevoe/UIAlertView-Blocks

Conflicts:
	RIButtonItem.h
	RIButtonItem.m